Depleted mantle-plume geochemical signatures: No paradox for plume theories
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Research Article| September 01, 1995 Depleted mantle-plume geochemical signatures: No paradox for plume theories Andrew C. Kerr; Andrew C. Kerr 1Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom Search for other works by this author on: GSW Google Scholar Andrew D. Saunders; Andrew D. Saunders 1Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom Search for other works by this author on: GSW Google Scholar John Tarney; John Tarney 1Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom Search for other works by this author on: GSW Google Scholar Neil H. Berry; Neil H. Berry 1Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom Search for other works by this author on: GSW Google Scholar Victoria L. Hards Victoria L. Hards 2Department of Geological Sciences, University of Durham, South Road, Durham DH1 3LE, United Kingdom Search for other works by this author on: GSW Google Scholar Geology (1995) 23 (9): 843–846. https://doi.org/10.1130/0091-7613(1995)023<0843:DMPGSN>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Andrew C. Kerr, Andrew D. Saunders, John Tarney, Neil H. Berry, Victoria L. Hards; Depleted mantle-plume geochemical signatures: No paradox for plume theories. Geology 1995;; 23 (9): 843–846. doi: https://doi.org/10.1130/0091-7613(1995)023<0843:DMPGSN>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract High-MgO liquids erupted in ocean-island settings and in some continental flood-basalt provinces commonly preserve a "depleted" composition, in terms of both highly incompatible trace elements and isotope ratios. These observations strongly imply that their source is also compositionally depleted. However, in at least one case (Iceland and the North Atlantic volcanic province), it can be shown that this depleted source is not the same as that feeding the present-day North Atlantic mid-ocean ridge. The depleted source must also have been much hotter than the mid-ocean ridge basalt (MORB) source to account for the volume of melt and primitive composition of some magmas that were generated. This depleted character, then, is an intrinsic component of mantle plumes, originating from the deep mantle. We propose that mantle plumes consist of a mixture of enriched or fusible streaks in a depleted, refractory matrix; preferential extraction of the enriched component occurs close to the plume axis. The depleted residue from this melting remains in the upper mantle and may therefore be a major contributor to the source region of MORB. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.Keywords:
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Mantle plume
Kingdom
Mantle plume
Flood basalt
Large igneous province
Asthenosphere
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SUMMARY The rise of mantle plumes to the base of the lithosphere leads to observable surface expressions, which provide important information about the deep mantle structure. However, the process of plume–lithosphere interaction and its surface expressions remain not well understood. In this study, we perform 3-D spherical numerical simulations to investigate the relationship between surface observables induced by plume–lithosphere interaction (including dynamic topography, geoid anomaly and melt production rate) and the physical properties of plume and lithosphere (including plume size, plume excess temperature, plume viscosity, and lithosphere viscosity and thickness). We find that the plume-induced surface expressions have strong spatial and temporal variations. Before reaching the base of the lithosphere, the rise of a plume head in the deep mantle causes positive and rapid increase of dynamic topography and geoid anomaly at the surface but no melt production. The subsequent impinging of a plume head at the base of the lithosphere leads to further increase of dynamic topography and geoid anomaly and causes rapid increase of melt production. After reaching maximum values, these plume-induced observables become relatively stable and are more affected by the plume conduit. In addition, whereas the geoid anomaly and dynamic topography decrease from regions above the plume centre to regions above the plume edge, the melt production always concentrates at the centre part of the plume. We also find that the surface expressions have different sensitivities to plume and lithosphere properties. The dynamic topography significantly increases with the plume size, plume excess temperature and plume viscosity. The geoid anomaly also increases with the size and excess temperature of the plume but is less sensitive to plume viscosity. Compared to the influence of plume properties, the dynamic topography and geoid anomaly are less affected by lithosphere viscosity and thickness. The melt production significantly increases with plume size, plume excess temperature and plume viscosity, but decreases with lithosphere viscosity and thickness.
Mantle plume
Asthenosphere
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Mantle plume
East African Rift
Hotspot (geology)
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We present results from a series of two‐dimensional numerical experiments in which synthetic melt compositions are calculated for a system in which a thermally buoyant, off‐axis mantle plume interacts with a nearby ridge axis. Spatial gradients in synthetic melt properties are compared to observed spatial gradients in geochemistry from the Easter–Salas y Gomez system in an effort to constrain the dynamics of mantle flow in off‐axis plume‐ridge systems. Results indicate that observed gradients in radiogenic isotopic ratios between the ridge axis and the plume require significant heating of the ambient mantle adjacent to the plume. This heating allows ambient mantle to melt off‐axis but also attenuates the flow from the plume to the ridge. When increases in viscosity due to dehydration during melting are considered, spatial gradients in the geochemical properties of synthetic melts become extremely sharp, at odds with the observational data. This may indicate that viscosity increases due to dehydration are not significant in off‐axis plume‐ridge systems.
Mantle plume
Radiogenic nuclide
Panache
Hotspot (geology)
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Abstract. Mid-ocean ridges and mantle plumes are two attractive windows to allow us to get a glimpse of mantle structure and dynamics. Dynamical interaction between ridge and plume processes have been widely proposed and studied, particularly in terms of ridge suction. However, the effects of plate drag on plumes and plume-ridge interaction remains poorly understood. Quantification of suction versus plate drag between ridges and plumes remains absent. Here we use 2D thermomechanical numerical models to study the plume-ridge interaction, exploring the effects of (i) the spreading rate of ridge, (ii) the plume radius, and (iii) the plume-ridge distance systematically. Our numerical experiments suggest two different geodynamic regimes: (1) plume motion prone to ridge suction is favored by strong buoyant mantle plume and short plume-ridge distance, and (2) plume migration driven by plate drag is promoted by fast-ridge spreading rate. Our results highlight fast-spreading ridges exert strong plate dragging force, rather than suction on plume motion, which sheds new light on the natural observations of plume absence along the fast-spreading ridges, such as the East Pacific Rises.
Mantle plume
Panache
Hotspot (geology)
Neutral buoyancy
Ridge push
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Mantle plume
Hotspot (geology)
Neutral buoyancy
Panache
Ridge push
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Abstract. The analysis of mid-ocean ridges and hotspots that are sourced by deep-rooted mantle plumes allows us to get a glimpse of mantle structure and dynamics. Dynamical interaction between ridge and plume processes have been widely proposed and studied, particularly in terms of ridgeward plume flow. However, the effects of plate drag on plume–lithosphere and plume–ridge interaction remain poorly understood. In particular, the mechanisms that control plume flow towards vs. away from the ridge have not yet been systematically studied. Here, we use 2D thermomechanical numerical models of plume–ridge interaction to systematically explore the effects of (i) ridge-spreading rate, (ii) initial plume head radius and (iii) plume–ridge distance. Our numerical experiments suggest two different geodynamic regimes: (1) plume flow towards the ridge is favored by strong buoyant mantle plumes, slow spreading rates and small plume–ridge distances; (2) plume drag away from the ridge is in turn promoted by fast ridge spreading for small-to-intermediate plumes and large plume–ridge distances. We find that the pressure gradient between the buoyant plume and spreading ridge at first drives ridgeward flow, but eventually the competition between plate drag and the gravitational force of plume flow along the base of the sloping lithosphere controls the fate of plume (spreading towards vs. away from the ridge). Our results highlight that fast-spreading ridges exert strong plate-dragging force, which sheds new light on natural observations of largely absent plume–lithosphere interaction along fast-spreading ridges, such as the East Pacific Rise.
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Hotspot (geology)
Ridge push
Panache
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Stratigraphic, petrological and geophysical studies suggest that the Late Permian (~ 260 Ma) Emeishan Large Igneous Province in southern China may be formed by mantle plume activity. However, the plume impingement hypothesis remains controversial since interpretations based on volcano-stratigraphic analyses around plume induced domal uplift/inner zone suggest that the volcanism occurred under submarine environment rather than elevated sub-aerial (above sea level) conditions, usually associated with the dynamic topography effects of the ascending mantle plumes. Here, 2-D numerical and 3-D scaled laboratory (analogue) plume experiments are used to explore the coupled dynamics of plume-mantle-lithosphere interaction and their evolution of surface topography characteristics. Experimental results show that the initial (plume incubation) phase is characterized by rapid, transient domal uplift above the plume axis, subsequently, as plume head flattens, there is short wavelength topographic variation (ie. subsidence and uplift occurs synchronously) due to the shear stress imposed onto the base of the lithosphere and loss of gravitational potential energy. The surface depressions predicted by the plume models, next to the plume axial/inner/uplift zone, may explain the deposition of submarine volcanics at Lake Erhai, Dali in the western side and Xiluo and Daqiao in the eastern side, which may resolve the plume controversy for the formation of Emeishan Large Igneous Province. Notably, while experimental results from these two different techniques show some differences, (e.g much bigger plume head for the laboratory experiment), the overall characteristics of the predictions have robust similarities. For instance, the extension above the plume axis may explain the enigmatic cause of the Panxi rift system, in the middle of the inner zone where giant dyke swarms radiate from, and mafic magma underplatings in the lower crust has been described by seismological studies.
Mantle plume
Large igneous province
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